Royston (Iceni) Weather Station

Daily Weather Observations - May 2007

It was a very dull and wet May in Royston, but temperatures were a little above average.

The drought of April continued into May until 6^th when a wet spell commenced and lasted up to 16^th. A drier interlude then intervened from 17^th to 25^th only to be followed by a very wet end to the month.

Total rainfall in May was an exceptionally high 147.5 millimetres, which is 314% of the 1971/2000 average. It was the wettest May in Royston since rainfall records began in the town in 1853, and followed the driest April since at least 1853! Also, it was the wettest month of any name since June 1958 when rainfall of 175.5 millimetres was recorded.

The wettest day of the month was 27^th with 65.7 millimetres rainfall. This was the wettest May day in Royston since at least 1972, the previous wettest May day having been 5^th May 1978 (52.5 millimetres rainfall). The number of "rain days" (0.2 millimetres or more) in May was 17, with rainfall equalling or exceeding 1.0 millimetre on 13 of these days. Rainfall duration in the month was 122.6 hours.

Despite the very dry April, the May rainfall brought the total for the year to date up to 310.0 millimetres, which is 141% of average.

Although the mean temperature in May was only 0.7°C above average it did mean that the run of warm May months was maintained and it was remarkably the 11^th consecutive warmer than average May. The mean daily maximum temperature in the month was 17.1°C, which is 0.1°C above average. The mean night minimum temperature of 8.6°C had the higher positive anomaly of 1.2°C.

The highest temperature recorded in May was 24.3°C on 24^th, whilst the lowest temperature recorded was 4.0°C on 2^nd. The 28^th was a particularly cold day for the end of May with a maximum temperature during daylight hours of only 7.0°C, and only 8.5°C over the whole 24 hour period. In contrast the night minimum temperature was as high as15.6°C on 24^th.

The lowest grass minimum temperature in May was 0.8°C on 1^st, meaning that ground frost was narrowly avoided in the month. The mean earth temperature at 30 cms depth as observed at 0900 GMT daily was 14.5°C. The maximum and minimum earth temperatures in the month were 17.7°C and 13.0°C on 25^th and 15^th respectively.

The month began with two very sunny days which accumulated no less than 27.9 hours sunshine, but unfortunately this did not herald a sunny month. Apart from two 2 day spells, 18^th/19^th and 22^nd/23^rd, which aggregated 46.1 hours sunshine, it was a mainly dull month thereafter. The sunshine total for May was 143.8 hours , which is 76% of the 1971/2000 average. The sunniest day of the month was 2^nd with 14.0 hours sunshine. Only 3 days in May were completely sunless.

It was the dullest May in Royston since at least 1997, and surprisingly the dullest of the 3 Spring months, March to May. In March sunshine was 33.3 hours higher than in May and in April the sunshine total was 88.4 hours higher than in May!

The mean wind speed in May was 2.4 mph, the highest daily (00/00 GMT) mean wind speed being 7.7 mph on 8^th and the lowest daily mean wind speed being 0.1 mph on 5^th and 20^th. The maximum wind gust speed in May was 46 mph on 10^th.

The analysis of wind directions as observed daily at 0900 GMT gives the following results: NORTH 6 days, NE 5, E 2, SE 0, S 3, SW 6, W 5, NW 3 and CALM 1.

The mean MSL air pressure in May was 1008.4 mB, peaking at 1022 mB on 23^rd and falling to its lowest value of 991 mB on 11^th.

At 1335 GMT on 22^nd relative humidity fell to 25%, its lowest value of the month. The highest daily (00/00 GMT) mean relative humidity in May was 99.7°C on 28^th, with a lowest daily mean value of 66.5% on 22^nd.

No fog (visibility < 1000 metres @ 0900 GMT) was observed in May.

SPRING (March/May) 2007: The mean daily maximum temperature in Spring was 15.8°C (+2.3), the mean night minimum temperature was 6.3°C (+1.2), rainfall was 185.3 millimetres (138%), and sunshine was 553.0 hours (125%). It was the warmest Spring in Royston since at least 1972, the wettest since 2001, and the sunniest since 2003.

Met. Observer, Royston (Iceni) Weather Station

5^th June 2007

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